This invention relates to an electronic control for an internal combustion engine, and more particularly to a method and apparatus for controlling the amount of fuel in a transient stage of operation of the engine of the type comprising an electronic-control fuel system such as an electronic fuel injection system or an electronic carburetor system.
The amount of fuel required in a transient stage of operation of the engine differs from that required in the steady operating condition of the engine. A control method is known which is applied to the control of the engine for the purpose of attaining optimized control of the amount of fuel injection in a transient stage of operation of the engine. According to this prior art control method, the intake pressure or the position of the throttle valve is sensed at predetermined time intervals to detect a variation thereof in the time interval, and, when the value of the detected variation becomes larger than a predetermined value, a fuel injection increase/decrease factor is obtained which is predetermined with respect to the engine cooling water temperature or which is predetermined with respect to the engine cooling water temperature and the intake manifold pressure (or the throttle position). Then, the value of the fuel injection increase-decrease factor thus obtained is used to correct the basic amount of fuel injection determined primarily by the rotation speed of the engine and the intake manifold pressure, thereby controlling the amount of fuel injection in a transient stage of operation of the engine.
In the prior art control method, the variation of the intake pressure or throttle position is generally detected at relatively long time intervals of, for example, several ten msec corresponding to the fuel injection time intervals. Therefore, when the prior art control method, in which the above variation is detected at the time intervals of several ten msec, is resorted to, the desired correction of the fuel injection meeting the variation of the amount of intake air supplied to the engine cannot be successfully attained in the case of, for example, abrupt acceleration in which the variation is completed within a short period of 2 msec to 30 msec. This is because, in such a case, the detected or computed rate of variation (the differential value) of the intake pressure or throttle position is smaller than the actual rate of variation of the variable.
Therefore, the prior art control method has been defective in that, with such a manner of controlling the amount of fuel injection in a transient stage of the engine operation, backfire of the engine occurs or a response speed is quite low when the temperature of engine cooling water is low.
The prior art control method has also been defective in that, when a micro-computer is used for the programmed control of the amount of fuel injection, a map is required, hence, many program words are required.